Design And Research Of Honeycomb Sandwich Engine Cover With Negative Poisson’s Ratio Material For Pedestrian Protection

As the modern automobile industry enters a new era,the number of domestic automobiles continues to grow positively.At the same time,the number of traffic accidents is also rising every year,which seriously endangers the safety of pedestrians and passengers.Therefore,the study of vehicle pedestrian protection technology can effectively improve the safety of pedestrians and minimize the damage caused by collision accidents.In the thesis,by analyzing the research status of engine hood design and negative Poisson ’s ratio material at home and abroad,the finite element model of head impactor is established according to the pedestrian protection standard law,and a new type of concave I-shaped honeycomb structure is proposed by using the negative Poisson ’s ratio metamaterial design theory,and its deformation mode and energy absorption characteristics are studied by numerical simulation.The multi-objective optimization of the crashworthiness of the structure is completed,and a negative Poisson ’ s ratio material honeycomb sandwich engine cover is designed.The research of this thesis mainly includes the following contents:1.Referring to the pedestrian protection standard GB/T24550-2009 and the pedestrian protection test in the C-NCAP2021 version,the finite element model of the pedestrian head impactor is established by using the nonlinear explicit dynamics software LS-DYNA and HyperWorks,and the benchmarking simulation verification is carried out,through the simplification and boundary processing of the whole vehicle model,the front-end model of the vehicle that meets the standard requirements is obtained,and the collision area of the head-shaped impactor is delineated.2.Based on the negative Poisson’s ratio metamaterial design theory,a new type of concave I-shaped honeycomb structure is proposed based on the concave hexagonal honeycomb structure.The numerical simulation is carried out by using software ABAQUS.The deformation mode and energy absorption and other dynamic responses of the honeycomb structure under in-plane and out-of-plane impact are studied,and the impact resistance of the concave I-shaped honeycomb structure is compared with that of the traditional hexagonal honeycomb structure and the concave hexagonal honeycomb structure,the comparison results show that the concave I-shaped honeycomb structure has good energy absorption characteristics and consistency of impact load.3.According to the dynamic impact characteristics of the concave I-shaped honeycomb,the response surface model is established,and the Pareto front is obtained by using the genetic algorithm NSGA-Ⅱ.While ensuring the simulation accuracy and calculation efficiency,the multi-objective optimization of the crashworthiness of the concave I-shaped honeycomb structure is completed,and the optimal design parameters are obtained.4.According to the optimal parameters of concave I-shaped honeycomb,the equivalent replacement model of honeycomb structure is established,and an engine cover with concave I-shaped honeycomb sandwich is designed.The original engine cover and two new engine covers with different sandwich thicknesses are simulated and compared by software LS-DYNA.The results show that the new engine cover has better pedestrian head protection performance and realizes its lightweight design.The research of this thesis has certain reference value for the design of negative Poisson ’ s ratio material and honeycomb sandwich engine cover.